Orientated polymeric devices

ABSTRACT

The present disclosure relates to a shape memory polymer material containing at least one two dimensional region having a first amount of stored stress in a first direction and a second amount of stored stress higher than the first amount of stored stress in a second direction, wherein the two dimensional region is capable of changing shape in only one of the first or second directions.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a PCT International Application claiming priority toU.S. Patent Application No. 60/912,740 filed on Apr. 19, 2007 and U.S.Patent Application No. 60/971,370 filed on Sep. 11, 2007, thedisclosures of which are incorporated herein by reference in theirentirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present disclosure relates generally to shape memory polymers and,more particularly, shape memory polymer material for use in fixatingmedical devices to bone.

2. Related Art

Sleeves of shape memory polymer material may be used in fixating medicaldevices to bone. These sleeves include a central through hole and areplaced on a medical device, such as an internal fixation device. Afterthe sleeve is placed on the device, the device is inserted into a boneand energy is then provided to the sleeve causing the sleeve to shrinkaxially and expand radially. This radial expansion and axial shrinkageof the sleeve allows the sleeve to engage both the device and the innerwall of the bone, thereby fixating the device to the bone.

However, it has been noticed, especially when the energy provided to thesleeve is in the form of a heat source that is placed within the throughhole of the sleeve, that the through hole expands, or relaxes away fromheat source and the device. This may result in inefficient heating ofthe sleeve, and thereby incomplete or uneven expansion of the sleeve,and device failure due to insufficient fixation of the device to thebone.

SUMMARY OF THE INVENTION

Further features, aspects, and advantages of the present disclosure, aswell as the structure and operation of various embodiments of thepresent disclosure, are described in detail below with reference to theaccompanying drawings.

In one aspect, the present disclosure relates to a shape memory polymermaterial containing at least one two dimensional region having a firstamount of stored stress in a first direction and a second amount ofstored stress higher than the first amount of stored stress in a seconddirection, wherein the two dimensional region is capable of changingshape in only one of the first or second directions.

In an embodiment, the material includes the shape of a cannulatedcylinder in which the two dimensional region has a shape of a contour ofthe cylinder. In another embodiment, the two dimensional region includesthe inner surface of the cylinder. In yet another embodiment, the twodimensional region is an outer surface of the cylinder. In a furtherembodiment, the two dimensional region is contained between an inner andan outer surface of the cylinder. In yet a further embodiment, thematerial includes a shape of a cannulated rectangle or square. In anembodiment, the first direction and the second direction areperpendicular to each other.

In another embodiment, the polymer material is resorbable. In yetanother embodiment, the polymer material is non-resorbable. In a furtherembodiment, the material includes a filler selected from a groupconsisting essentially of hydroxyapatite, calcium carbonate, andtricalcium phosphate. In yet a further embodiment, the material includesa porogen selected from a group consisting essentially of sodiumchloride, lithium bromide, lithium iodide, calcium chloride, sodiumiodide, magnesium sulphate, and calcium sulphate.

In an embodiment, the polymer material includes a polyester selectedfrom a group including P(L)LA, poly (D) lactic acid (P(D)LA), poly (DL)lactic acid (P(DL)LA), poly(L-co-DL) lactic acid (P(LDL)LA), poly (L)lactic acid-co-glycolide (P(L)LGA)), poly (DL) lactic acid-co-glycolide(P(DL)LGA)),poly (D) lactic acid-co-glycolide (P(D)LGA)),polycaprolactone (PCL), PGA, and combinations thereof. In anotherembodiment, the material includes a polyacrylate. In yet anotherembodiment, the material includes a polymethyl methacrylate polymer orcopolymer thereof. In a further embodiment, the material includes apolybutyl methacrylate polymer or copolymer thereof. In yet a furtherembodiment, the material includes a polybutyl methacrylate-co-polymethylmethacrylate copolymer. In an embodiment, the material includes apolystyrene copolymer.

In another aspect, the present disclosure relates to a rod having afirst amount of stored radial stress located on an inner surface regionof the rod and a second amount of stored radial stress higher than thefirst amount located on an outer surface region of the rod. In anembodiment, the outer surface expands radially and the inner surfaceremains unchanged upon providing energy to the rod.

In yet another aspect, the present disclosure relates to a cannulatedrod having a shape memory polymer material wherein the rod includes afirst amount of stored radial stress located on an inner surface regionof the rod and a second amount of stored radial stress higher than thefirst amount located on an outer surface region of the rod. In anembodiment, the outer surface expands radially and the inner surfacecontracts radially upon providing energy to the rod.

In a further aspect, the present disclosure relates to a method offixating an internal fixation device to bone. The method includesproviding an internal fixation device having a sleeve of shape memorypolymer material coupled to the device; inserting the internal fixationdevice into the bone; and providing energy to the sleeve of shape memorypolymer material, wherein an outer diameter of the sleeve increases toengage an inner wall of the bone and an inner diameter of the sleevedecreases to engage the fixation device.

In yet a further aspect, the present disclosure relates to a method offixating an internal fixation device to bone. The method includesproviding an internal fixation device having a sleeve of shape memorypolymer material coupled to the device; inserting the internal fixationdevice into the bone; and providing energy to the sleeve of shape memorypolymer material, wherein an outer diameter of the sleeve increases toengage an inner wall of the bone and an inner diameter of the sleeveremains unchanged.

In an aspect, the present disclosure relates to a method of deforming asleeve of shape memory polymer material. The method includes providing asleeve of shape memory polymer material having an outer diameter and aninner diameter; and providing energy to the sleeve to deform the sleeve,wherein the outer diameter of the sleeve increases and the innerdiameter of the sleeve decreases or remains unchanged.

In another aspect, the present disclosure relates to an internalfixation device including an interface portion; and a sleeve of shapememory polymer material coupled to the interface portion.

In a further aspect, the present disclosure relates to a shape memorypolymer material having a tailored stress pattern that allows thematerial to expand and contract simultaneously.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and form a part ofthe specification, illustrate the embodiments of the present disclosureand together with the description, serves to explain the principles ofthe disclosure. In the drawing:

FIG. 1A shows a perspective view of a first embodiment of a compressionmold set.

FIG. 1B shows a perspective view of a second embodiment of a compressionmold set.

FIG. 2A shows a perspective view of a first embodiment of a die drawingrig.

FIG. 2B shows a perspective view of a second embodiment of a die drawingrig.

FIGS. 3A-3C show frontal views of polymer sleeves of the presentdisclosure before and after deformation of the sleeves.

FIGS. 4A-4B show cross-sectional views of a medical device including apolymer sleeve of the present disclosure both before and afterdeformation of the sleeve.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The following description of the preferred embodiment(s) is merelyexemplary in nature and is in no way intended to limit the disclosure,its application, or uses.

The present disclosure relates to sleeves of shape memory polymermaterial having tailored expansion properties that are designed toimprove the functional performance of the sleeve. Upon providing thesleeve with energy, the sleeve deforms in a pre-programmed manner suchthat it enhances contact with surfaces surrounding the sleeve, such asthe surface of the device and/or the inner surface of the bone. Thesesleeves and the process for making them are provided in the followingexamples.

Example One

A first billet including a composite of poly(D-lactic acid-co-glycolicacid) (PDLAGA) and 35% calcium carbonate (CaCO3) was produced bycompression molding. The billet was 20 mm in diameter and 150 mm inlength. A drill was used to create a hole, approximately 6 mm indiameter and 70 mm in length, in one end of the billet, and the otherend of the billet was prepared for die drawing. A stainless steel rod,about 6 mm in diameter and 200 mm in length, was inserted into thebillet and the entire billet-rod assembly was drawn through a 12 mm dieat 75° C. and at 1 mm per minute. After drawing, the billet was cut intosections, approximately 30 mm long, with a hand hacksaw. The metal rodwas subsequently removed from each section using a 4 mm steel rod and a4 oz ball hammer.

A second billet, including the same dimensions and composite, was alsoproduced by compression molding. The billet was die drawn through a 10mm die at 75° C. to produce a billet having a 10 mm diameter. A drillwas used to create a hole, approximately 4 mm in diameter, into thedrawn billet.

For the purposes of this disclosure, both of the drawn billets representthe sleeves of shape memory polymer material described above. Samples ofboth drawn billets were then immersed in hot water (80° C.) for 10minutes to relax or deform the billets. The samples were then removedand allowed to cool to room temperature for 5 minutes. The relaxedbillets were found to have the dimensions shown in Table 1.

TABLE 1 Drawn Relaxed First Billet OD (mm) 12.1 ± 0.1  18.6 ± 0.1  ID(mm) 5.9 ± 0.1 5.8 ± 0.1 Second Billet OD (mm) 9.6 ± 0.1 17.5 ± 0.1  ID(mm) 4.4 ± 0.1 6.1 ± 0.1

As shown in Table 1, the outer diameter of both billets and the innerdiameter of the second billet increased significantly when the billetswere provided with energy. However, the inner diameter of the firstbillet did not change upon providing the first billet with energy. FIGS.3A-3B helps to explain this result. FIG. 3A shows a front view of abillet representing either the first or the second billet describedabove. The billet shows three different regions. Region 70 is the billithole, region 80 is the inner diameter, and region 90 is the outerdiameter. It is believed that drawing the first billet in the presenceof the steel rod resulted in an uneven radial stress pattern betweenregions 80 and 90. Specifically, it is believed that the radial stressstored in region 80 of the billet located adjacent to the rod (the areaof the inner diameter) was very low, the radial stress stored in region90 of the billet located adjacent to the die interface was highercompared to region 90, and the material located between regions 80,90had a varying level of stored radial stress depending on their proximityto regions 80,90. Therefore, the polymer in region 80, unlike thepolymer in region 90, did not contain the shape memory qualities (storedstress) required for the inner diameter to change shape or expandradially upon providing the billet with energy, as shown in FIG. 3B.Since the inner diameter of the billet did not increase upon providingthe billet with energy, it is believed that this type of billet wouldsubstantially reduce the above problems when the billet is used inconnection with a medical device, namely inefficient heating of thebillet and insufficient fixation of the device to bone.

In addition to the radial stress referred to above, stored stress wouldalso be present along the length of the billet. This type of stress isreferred to as axial stress. Therefore, each of regions 80,90 and theregions therebetween can be referred to as two-dimensional regionshaving one direction (radial) and another direction (axial) that areperpendicular to one another. Due to the billet shrinking axially uponproviding the billet with energy, it is believed that the stored axialstress in regions 80,90 and therebetween is higher than at least theradial stress stored in region 80 of the billet. For the purposes ofthis disclosure, the axial stress in region 80 is higher than 0 and theradial stress in region 80 is about 0.

Example Two

A composite material of PLLA-co-DL and 35% calcium carbonate (CaCO₃) waspre-dried overnight at a temperature of 50° C. using a Motan model LuxorCA15 hot air desiccant dryer. A compression mold set 10, shown in FIG.1A, was used to compress the dried material. The mold set 10 includes abase plate 11 coupled to a mold body 12 having a through hole 13.Located within the through hole 13 of the mold body 12 is a spigotshaping insert 14. A plunger 15 is used to compact the material, as willbe further described below. The through hole 13 is about 30 mm indiameter and the mold body has a length of about 300 mm and an outerdiameter of about 75 mm. Although not shown, the spigot shaping insert14 has a lead in diameter of 29.5 mm and continues to a final diameterof the intended drawn product. The insert 14 is 25 mm in length.

Prior to use, two 750 W heater bands were placed on the mold body 12 andthe mold body 12 was heated to 165° C. for 20 minutes. The dried polymercomposite material was then placed into the through hole of the heatedmold body 12. The material was compacted by inserting the plunger 15into the through hole 13 and applying a light load (<1000 N) on theplunger 15 via the use of an instron machine. This routine was repeateduntil the through hole 13 was completely filled with material. Thematerial was compressed by applying a load of 3.5 kN to the plunger 15via the use of a computer controlled Messphysik model Beta 20-10/8×15testing machine. The heater bands were turned off and the mold 10 wasallowed to cool while under a constant load of 3.5 kN. The load wasreleased when the temperature of the mold 10 reached 50° C. The unloadedmold 10 was left to cool overnight. After cooling, the mold 10 wasremoved from the mechanical test machine and the base plate 11 wasremoved. The mold 10 was then was then transferred to a hydraulic press,which was used to push the spigot insert 14 and a molded billet out ofthe mold body 12.

The billet was then die drawn using a drawing rig 20 shown in FIG. 2A.The rig 20 includes a base portion 21, a die retainer 22, and a chamber23. The chamber 23 includes chamber doors 24 that are closed during thedie drawing process. A drawing die 25, including a through hole 26having a diameter of 30 mm at the entrance 26 a to the through hole 26and a diameter of 15 mm at the exit 26 b from the through hole 26, islocated in the die retainer 22.

The base portion 21 was coupled to the platform of a computer Messphysikmodel Beta 20-10/8×15 testing machine using the location post. A 650 Wheater band was clamped to the outside of the die retainer 22 of the rig20. The billet was loaded into the rig 20 so that the spigot shapinginsert 14 extended from the die 25. A clamp was attached to the crosshead of the testing machine and subsequently coupled to the spigot 14 toprepare the spigot 14 for drawing. A hot air gun, (Steinel type 3483),with a set temperature of 70° C. was attached to the chamber doors 24via a cowling (not shown). The drawing process was commenced when thedie retainer had maintained a temperature of 75° C. for 20 minutes. Thecrosshead speed was set at 10 mm/min for the first 40 mm of drawing andthen increased to 30 mm/min for the rest of the drawing process. The diedrawn billet (15 mm diameter) was collected and a small 25 mm long plugwas cut from the billet. A through hole (8 mm) was then drilled throughthe centre of the billet.

A second billet was made via a very similar process to the first billet.However, as shown in FIG. 1B, the mold 10 was assembled with a mandrelpin 16. The pin 16 includes a base 16 a having a similar diameter tothat of the through hole 13 and a shaft 16 b having a first end 16 b′coupled to the base 16 a and a second end 16 b″. The pin 16 is locatedin the through hole 13 such that the second end 16 b″ of the pin 16extends out of the mold body 12. Prior to use, the spigot shaping insert14 was placed within the through hole 13 such that it was disposed onthe shaft 16 b of the pin 16. The plunger 15 included a hole 15 a thatwas configured to fit over the shaft 16 during compaction andcompression of the material. After compaction and compression of thematerial, as described above, the pin 16 and billet were extracted fromthe mold body 12 and the pin 16 was subsequently removed from thebillet. A billet was produced having a 6 mm central through hole.

The second billet was then die drawn using a drawing rig 20 shown inFIG. 2B. The rig 20 includes a base portion 21, a die retainer 22, and achamber 23. The chamber 23 includes chamber doors 24 that are closedduring the die drawing process and a chuck 28 for holding a mandrel, aswill be described later. A drawing die 25, including a through hole 26having a diameter of 30 mm at the entrance 26 a to the through hole 26and a diameter of 15 mm at the exit 26 b from the through hole 26, islocated in the die retainer 22.

The base portion 21 was coupled to the platform of a computer Messphysikmodel Beta 20-10/8×15 testing machine using the location post. A 650 Wheater band was clamped to the outside of the die retainer 22 of the rig20. The billet was loaded into the rig 20 so that the spigot shapinginsert 14 extended from the die 25. A mandrel 27 was inserted into thebillet prior to placing the billet in the rig 20. The mandrel 27includes a first portion 27 a that was held in place via use of thechuck 28 and a second portion 27 b having a wider diameter (8 mm) and atransition from the wider diameter to the diameter of the first portion27 a through a 30° taper. The mandrel 27 was positioned such that thesecond portion 27 b laid approximately level with the through hole exit26 b or about 1 mm short of it. A clamp was attached to the cross headof the testing machine and subsequently coupled to the spigot 14 toprepare the spigot 14 for drawing. A hot air gun, (Steinel type 3483),with a set temperature of 70° C. was attached to the chamber doors 24via a cowling (not shown). The drawing process was commenced when thedie retainer had maintained a temperature of 75° C. for 20 minutes. Thecrosshead speed was set at 10 mm/min for the first 40 mm of drawing andthen increased to 30 min/min for the rest of the drawing process. Thedie drawn billet (15 mm diameter) was collected and a small 25 mm longplug was cut from the billet. The drawn billet had an 8 mm centralthrough hole.

For the purposes of this disclosure, both of the drawn billets representthe sleeves of shape memory polymer material described above. Samples ofthe billet that was drawn without the use of a mandrel (Sample A) and ofthe billet that was drawn with the use of a mandrel (Sample B) were eachplaced in hot water (95° C.) for 10 minutes. The outer diameters ofsamples A and B and the outer diameter of sample A expanded to diametersof 27 mm, 27 mm, and 14 mm, respectively. However, the inner diameter ofSample B decreased to 5.7 mm. FIGS. 3A and 3C help to explain this. FIG.3A shows a front view of a billet representing either the Sample Abillet or the Sample B billet described above. The billet shows threedifferent regions. Region 70 is the billet hole, region 80 is the innerdiameter, and region 90 is the outer diameter. It is believed that whenSample B billet was drawn in the presence of the mandrel, oppositeradial stress patterns between region 80 and region 90 resulted.Specifically, it is believed that the radial stress stored in region 80of the billet adjacent to the mandrel was in opposite direction to thestored radial stress generated in region 90 located adjacent to the dieinterface. Therefore, upon providing energy to the billet, the billetexpands radially such that region 90, corresponding to the outerdiameter, increases and region 80, corresponding to the inner diameter,contracts or decreases radially, as shown in FIG. 3C. Since the radialstress stored in regions 80,90 are opposite to one another, it isbelieved that there is zero, or a very small amount of radial storedstress, located between regions 80,90.

In addition to the radial stress referred to above, stored stress wouldalso be present along the length of the billet. This type of stress isreferred to as axial stress. Therefore, each of regions 80,90 and theregions therebetween can be referred to as two-dimensional regionshaving one direction (radial) and another direction (axial) that areperpendicular to one another. Due to the billet shrinking axially uponproviding the billet with energy, it is believed that the stored axialstress in regions 80,90 and therebetween is higher than at least theradial stress stored in region 80 of the billet. For the purposes ofthis disclosure, the axial stress in region 80 is higher than 0 and theradial stress in region 80 is about 0.

Drawing a billet through a mandrel, similar to the mandrel describedabove, but with a die having the same diameter as the outer surface ofthe billet is also within the scope of this disclosure. In this case, aradial stored stress would be present region 80 and no or a smalleramount of stress compared to region 80, would be present in region 90.Axial stored stress would still be present in regions 80,90. However, itis believed that the axial stored stress in region 90 would be higherthan at least the radial stored stress in region 90 of the billet. Forthe purposes of this embodiment, the axial stress in region 90 is higherthan 0 and the radial stress is about 0.

Since the inner diameter of the billet decreased radially upon providingthe billet with energy, it is believed that this type of billet wouldsubstantially reduce the above problems when the billet is used inconnection with a medical device, namely inefficient heating of thebillet and insufficient fixation of the device to bone. This benefit isshown in FIGS. 4A and 4B. A sleeve of shape memory polymer material 31,such as the sleeve 31 described above for Sample B, is coupled to aninterface portion 42 of an internal fixation device 41, such as anintramedullary nail, and the internal fixation device 41 is insertedinto bone 51. The sleeve 31 is then provided with energy to deform thesleeve 31. A decrease in the inner diameter 31 a of the sleeve 31 causesthe sleeve 31 to grip the device 41 and an increase in the outerdiameter 31 b causes the outer diameter 31 b to contact the bone 51,thereby filling the gap 61 between the bone 51 and the fixation device41. As can be seen in FIG. 4B, axial shrinkage of the sleeve 31 alsooccurs.

The interface portion 42 of the fixation device 41 is the portion of thedevice 41 that the sleeve 31 is coupled to or interfaces with. Thisportion may be located anywhere along the length of the device 41 andmay be of a lesser diameter than the rest of the device 41 or the samediameter as the rest of the device 41. A surface of the interfaceportion 42 may include texture, such as grooves, engravings, or othertypes of texture that would allow further engagement of the sleeve 31 tothe device 41. In addition, the interface portion 42 may be machined tohave any shape. The shapes and surfaces may be machined, molded, cast,laser cut, or chemically etched into the internal fixation device 41 orformed via another method known to one of ordinary skill in the art.

Instead of using the sleeve of shape memory polymer material describedabove for Sample B, the sleeve described above for the first billet mayalso be used. In this case, as described above, once the sleeve isprovided with energy, the outer diameter would increase to engage thebone and the inner diameter would remain unchanged. Hence, the sleevewould fixate the device to the bone and coupling of the sleeve to thedevice would remain unchanged.

The sleeves described above and shown in the figures are cylindrical.However, the sleeves may be other shapes including, without limitation,rectangular or square.

For the purposes of this disclosure, the polymer includes PDLAGA andPLLA-co-DL. However, any biocompatible, shape memory polymeric materialmay be used, including, an amorphous polymer, a semi-crystallinepolymer, and combinations thereof. Specific polymer may include, withoutlimitation, poly-alpha-hydroxy acids, polycaprolactones, polydioxanones,polyesters, polyglycolie acid, polyglycols, polylactides,polyorthoesters, polyphosphates, polyoxaesters, polyphosphoesters,polyphosphonates, polysaccharides, polytyrosine carbonates,polyurethanes, polyacrylic/polyacrylates, polymethyl methacrylate,polybutyl methacrylate, polybutyl methacrylate-co-polymethylmethacrylate, polyethyl methacrylate, polybutylacrylate, polystyrene,polyolefin, polyethylene, poly-alpha-hydroxy acids, and copolymers orpolymer blends thereof. Polyesters that may be used include P(L)LA, poly(D) lactic acid (P(D)LA), poly (DL) lactic acid (P(DL)LA), poly(L-co-DL)lactic acid (P(LDL)LA), poly (L) lactic acid-co-glycolide (P(L)LGA)),poly (DL) lactic acid-co-glycolide (P(DL)LGA)),poly (D) lacticacid-co-glycolide (P(D)LGA)), polycaprolactone (PCL), PGA, andcombinations thereof. In addition, the polymer may be resorbable ornon-resorbable.

Also for the purposes of this disclosure, the composite includes calciumcarbonate as a filler material. However, other filler materials may alsobe used, including, without limitation, tricalcium phosphate (TCP),calcium sulphate, carbon nanotubes, degradable ceramic, and degradableglass. In addition, the rod used in connection with the billet duringthe die drawing process, as described above, is a stainless steel rod.However, the rod may be of another material, including, withoutlimitation, plastic, ceramic, or combinations thereof. The rod may alsohave a range of cross-sectional profiles, including, without limitation,round, square, star-shaped, and triangular. In addition, the rod mayhave a consistent cross-sectional area or a varying cross-sectional areaand the surface of the rod may be smooth or have a pattern to allow thedrawn polymer billet to integrate with the surface.

Examples of adding energy to the polymer material include electrical andthermal energy sources, the use of force, or mechanical energy, and/or asolvent. Any suitable force that can be applied either preoperatively orintra-operatively can be used. One example includes the use of ultrasonic devices, which can relax the polymer material with minimal heatgeneration. Solvents that could be used include organic-based solventsand aqueous-based solvents, including body fluids. Care should be takenthat the selected solvent is not contra indicated for the patient,particularly when the solvent is used intra-operatively. The choice ofsolvents will also be selected based upon the material to be relaxed.Examples of solvents that can be used to relax the polymer materialinclude alcohols, glycols, glycol ethers, oils, fatty acids, acetates,acetylenes, ketones, aromatic hydrocarbon solvents, and chlorinatedsolvents.

The polymeric material may include a composite or matrix havingreinforcing material or phases such as glass fibers, carbon fibers,polymeric fibers, ceramic fibers, ceramic particulates, rods, platelets,and fillers. Other reinforcing material or phases known to one ofordinary skill in the art may also be used. In addition, the polymericmaterial may be made to porous via the use of porogens. The porogensinclude sodium chloride, lithium bromide, lithium iodide, calciumchloride, sodium iodide, magnesium sulphate, and calcium sulphate.Porosity may allow infiltration by cells from surrounding tissues,thereby enhancing the integration of the material to the tissue. Also,one or more active agents may be incorporated into the material.Suitable active agents include bone morphogenic proteins, antibiotics,anti-inflammatories, angiogenic factors, osteogenic factors,monobutyrin, thrombin, modified proteins, platelet rich plasma/solution,platelet poor plasma/solution, bone marrow aspirate, and any cellssourced from flora or fauna, such as living cells, preserved cells,dormant cells, and dead cells. It will be appreciated that otherbioactive agents known to one of ordinary skill in the art may also beused. Preferably, the active agent is incorporated into the polymericshape memory material, to be released during the relaxation ordegradation of the polymer material. Advantageously, the incorporationof an active agent can act to combat infection at the site ofimplantation and/or to promote new tissue growth.

For the purposes of this disclosure, the sleeves are used in medicalapplications. However, sleeves for use in non-medical applications arealso within the scope of this disclosure.

In view of the foregoing, it will be seen that the several advantages ofthe disclosure are achieved and attained.

The embodiments were chosen and described in order to best explain theprinciples of the disclosure and its practical application to therebyenable others skilled in the art to best utilize the disclosure invarious embodiments and with various modifications as are suited to theparticular use contemplated.

As various modifications could be made in the constructions and methodsherein described and illustrated without departing from the scope of thedisclosure, it is intended that all matter contained in the foregoingdescription or shown in the accompanying drawings shall be interpretedas illustrative rather than limiting. Thus, the breadth and scope of thepresent disclosure should not be limited by any of the above-describedexemplary embodiments, but should be defined only in accordance with thefollowing claims appended hereto and their equivalents.

1. A shape memory polymer material containing at least one twodimensional region having a first amount of stored stress in a firstdirection and a second amount of stored stress higher than the firstamount of stored stress in a second direction, wherein the twodimensional region is capable of changing shape in only one of the firstor second directions.
 2. The shape memory polymer material of claim 1wherein the material includes the shape of a cannulated cylinder inwhich the two dimensional region has a shape of a contour of thecylinder.
 3. The shape memory polymer material of claim 2 in which thetwo dimensional region includes the inner surface of the cylinder. 4.The shape memory polymer material of claim 2 in which the twodimensional region is an outer surface of the cylinder.
 5. The shapememory material of claim 2 in which the two dimensional region iscontained between an inner and an outer surface of the cylinder.
 6. Theshape memory polymer material of claim 1 wherein the material includesshape of a cannulated rectangle or square.
 7. The shape memory polymermaterial of claim 1 wherein the first direction and the second directionare perpendicular to each other.
 8. A cannulated rod including a shapememory polymer material wherein the rod includes a first amount ofstored radial stress located on an inner surface region of the rod and asecond amount of stored radial stress higher than the first amountlocated on an outer surface region of the rod.
 9. The cannulated rod ofclaim 8 wherein the outer surface expands radially and the inner surfaceremains unchanged upon providing energy to the rod,
 10. (canceled) 11.(canceled)
 12. A method of fixating an internal fixation device to bonecomprising: providing an internal fixation device having a sleeve ofshape memory polymer material coupled to the device; inserting theinternal fixation device into the bone; providing energy to the sleeveof shape memory polymer material, wherein an outer diameter of thesleeve increases to engage an inner wall of the bone and an innerdiameter of the sleeve decreases to engage the fixation device.
 13. Amethod of fixating an internal fixation device to bone comprising:providing an internal fixation device having a sleeve of shape memorypolymer material coupled to the device; inserting the internal fixationdevice into the bone; providing energy to the sleeve of shape memorypolymer material, wherein an outer diameter of the sleeve increases toengage an inner wall of the bone and an inner diameter of the sleeveremains unchanged.
 14. A method of deforming a sleeve of shape memorypolymer material comprising: providing a sleeve of shape memory polymermaterial having an outer diameter and an inner diameter; providingenergy to the sleeve to deform the sleeve, wherein the outer diameter ofthe sleeve increases and the inner diameter of the sleeve decreases orremains unchanged.
 15. An internal fixation device comprising: aninterface portion; and a sleeve of shape memory polymer material coupledto the interface portion.
 16. A shape memory polymer material having atailored stress pattern that allows the material to expand and contractsimultaneously.
 17. The material of claim 1 wherein the polymer materialis resorbable.
 18. The material of claim 1 wherein the polymer materialis non-resorbable.
 19. The material of claim 1 wherein the materialincludes a filler selected from a group consisting essentially ofhydroxyapatite, calcium carbonate, and tricalcium phosphate.
 20. Thematerial of claim 1 wherein the material includes a porogen selectedfrom a group consisting essentially of sodium chloride, lithium bromide,lithium iodide, calcium chloride, sodium iodide, magnesium sulphate, andcalcium sulphate.
 21. The material of claim 1 wherein the polymermaterial includes a polyester selected from a group including P(L)LA,poly (D) lactic acid (P(D)LA), poly (DL) lactic acid (P(DL)LA),poly(L-co-DL) lactic acid (P(LDL)LA), poly (L) lactic acid-co-glycolide(P(L)LGA)), poly (DL) lactic acid-co-glycolide (P(DL)LGA)),poly (D)lactic acid-co-glycolide (P(D)LGA)), polycaprolactone (PCL), PGA, andcombinations thereof.
 22. The material of claim 1 wherein the materialincludes a polyacrylate.
 23. The material of claim 1 wherein thematerial includes a polymethyl methacrylate polymer or copolymerthereof.
 24. The material of claim 1 wherein at least one or both of theat least one polymer component and the second polymer component includesa polybutyl methacrylate polymer or copolymer thereof.
 25. The materialof claim 1 wherein the material includes a polybutylmethacrylate-co-polymethyl methacrylate copolymer.
 26. The material ofclaim 1 wherein the material includes a polystyrene copolymer.